fix(pulse-monitor): reset heartbeat after tool execution to prevent false positives

Tools can take arbitrary time, so we need a fresh baseline after execution.
Previously, lastHeartbeat wasn't updated after tool.execute.after, causing
stalled detection to trigger immediately after long-running tools.

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/pulse-monitor.ts

@@ -132,8 +132,13 @@ export function createPulseMonitorHook(ctx: PluginInput) {
         // Pause monitoring while tool runs locally (tools can take time)
         stopMonitoring()
     },
-    "tool.execute.after": async (_input: { sessionID: string }) => {
-        // Don't forcefully restart monitoring here to avoid false positives
+    "tool.execute.after": async (input: { sessionID: string }) => {
+        // Reset heartbeat after tool execution to prevent false positives
+        // Tools can take arbitrary time, so we need a fresh baseline
+        if (input.sessionID && currentSessionID === input.sessionID) {
+            lastHeartbeat = Date.now()
+        }
+        // Don't forcefully restart monitoring here
         // Monitoring will naturally resume when next session/message event arrives
         // This prevents stalled detection on legitimately idle sessions
     }